[Bug target/50583] Many __sync_XXX builtin functions are incorrect

["hjl.tools at gmail dot com" <gcc-bugzilla at gcc dot gnu dot org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50583

--- Comment #1 from H.J. Lu <hjl.tools at gmail dot com> 2011-09-30 16:57:14 UTC ---
We have 2 choices:

1. Update document of

`TYPE __sync_fetch_and_add (TYPE *ptr, TYPE value, ...)'
`TYPE __sync_fetch_and_sub (TYPE *ptr, TYPE value, ...)'
`TYPE __sync_fetch_and_or (TYPE *ptr, TYPE value, ...)'
`TYPE __sync_fetch_and_and (TYPE *ptr, TYPE value, ...)'
`TYPE __sync_fetch_and_xor (TYPE *ptr, TYPE value, ...)'
`TYPE __sync_fetch_and_nand (TYPE *ptr, TYPE value, ...)'

to

 {
   tmp = *ptr;
   tmp1 = tmp OP value;
   return __sync_val_compare_and_swap (ptr, tmp, tmp1);
 }

2. Remove those __sync_fetch_and_XXX which aren't

 { tmp = *ptr; *ptr OP= value; return tmp; }

Since only

 { tmp = *ptr; *ptr OP= value; return tmp; }

can be used to implement locks, I think we should do 2.